1. Field of the Invention
This invention relates to methods and systems for controlling an amount of fuel delivered to an individual engine cylinder during transient engine operating conditions.
2. Background Information
Under a steady-state operating condition of an internal combustion engine, the mass of the air charge for each cylinder event is constant. The fuel transport mechanisms in the fuel intake have reached near equilibrium conditions, allowing a constant mass of injected fuel for each combustion event in each cylinder. However, when the engine operating condition is not steady-state, such as in an acceleration mode or deceleration mode, the mass of injected fuel required to achieve the desired air/fuel ratio in each cylinder is not constant as a result of transients in the mass of air charge being delivered to the cylinders.
Various attempts have been made to improve control of air/fuel ratios during transient engine conditions. For example, U.S. Pat. No. 5,746,183 describes control of fuel mass based on a fuel puddle model representative of a fuel puddle that theoretically is present in the intake manifold. The fuel puddle model uses a first order X and tau coupled inverse compensator model of the fuel puddle to control transient fuel compensation. For example, an initial estimate of desired fuel mass of the puddle per cylinder embodies a fuel/air function (f_a_ratio[n]) that represents a desired in-cylinder fuel-air ratio for that cylinder""s bank and comprises a closed loop input to the inverse compensator mathematics from another section of the engine control routine.
The dynamic response of the inverse compensator model is limited by the model and mathematical constraints imposed by the model (e.g. the coupling between X and tau as well as use of single X and tau values for both acceleration and deceleration modes) and as a result may encounter difficulty in responding to different drivability requirements associated with acceleration and deceleration modes of engine operation. The model-based control system is designed to provide mandatory fuel compensation during the engine crank mode. The mandatory fuel compensation during engine crank mode has resulted in increased calibration efforts to make this system responsive, primarily due to the interaction between transient compensation and crank fuel calculation.
The present invention provides a method and system for controlling fuel mass during transient engine conditions that is based on a transient fuel compensation algorithm that provides transient fuel compensations that address drivability requirements associated with the acceleration mode and deceleration mode of engine operation as well as the cranking mode of engine operation.
In accordance with an illustrative embodiment of the invention, a method and system for determining fuel mass to be delivered to each cylinder of an internal combustion engine during transient engine operation involve determining a desired in-cylinder fuel mass for combustion based on a plurality of engine parameters, determining whether a current mode of engine operation is an acceleration mode or a deceleration mode, and determining a transient fuel mass compensation factor (mf_tfc[inj]) in response to the determined current acceleration or deceleration mode of engine operation. The transient fuel mass compensation factor and a base desired in-cylinder fuel mass (calculated from fuel air ratio) are combined to provide a desired injected fuel mass for the next combustion event for each cylinder.
In a particular embodiment of the invention, the desired in-cylinder fuel mass for combustion is determined from engine parameters representing air charge, feedforward air-fuel demand, and air/fuel stoichiometric ratio.
In another particular embodiment of the invention, the determination of the current mode of engine operation is made by comparing the desired in-cylinder fuel mass for combustion and a filtered desired in-cylinder fuel mass obtained using the prior injection history of each cylinder and a time constant determined in response to the determined current acceleration or deceleration mode of engine operation.
In still another particular embodiment of the invention, the determination of a transient fuel mass compensation factor is made by obtaining a difference between the desired in-cylinder fuel mass for combustion and the filtered desired in-cylinder fuel mass and multiplying the difference by a value of a gain multiplier determined in response to the determined current acceleration or deceleration mode of engine operation.
In still another particular embodiment of the invention, the method and system of the invention optionally can force the transient fuel compensation factor to zero during an engine crank mode such that no fuel transient compensation is conducted during the engine crank mode.
The present invention is advantageous for determining transient fuel compensations for each cylinder independently for the acceleration mode or deceleration mode of engine operation to improve drivability and avoids transient fuel compensation during the engine crank mode, reducing calibration requirements for the method and system.
The above advantages of the present invention will become more readily apparent from the following description taken with the following drawings.